WO1998016090A1 - Chalumeau a arc de plasma et procede utilisant un systeme de demarrage a contact - Google Patents

Chalumeau a arc de plasma et procede utilisant un systeme de demarrage a contact Download PDF

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Publication number
WO1998016090A1
WO1998016090A1 PCT/US1997/016318 US9716318W WO9816090A1 WO 1998016090 A1 WO1998016090 A1 WO 1998016090A1 US 9716318 W US9716318 W US 9716318W WO 9816090 A1 WO9816090 A1 WO 9816090A1
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WO
WIPO (PCT)
Prior art keywords
nozzle
electrode
torch
spring element
invention according
Prior art date
Application number
PCT/US1997/016318
Other languages
English (en)
Inventor
Zhipeng Lu
Original Assignee
Hypertherm, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hypertherm, Inc. filed Critical Hypertherm, Inc.
Priority to JP51753598A priority Critical patent/JP4267704B2/ja
Priority to CA002268102A priority patent/CA2268102C/fr
Priority to EP97943315A priority patent/EP0941640B1/fr
Priority to DE69737201T priority patent/DE69737201T2/de
Priority to AU44814/97A priority patent/AU727927B2/en
Publication of WO1998016090A1 publication Critical patent/WO1998016090A1/fr

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/3489—Means for contact starting

Definitions

  • the present invention relates to plasma arc torches and methods of operation, and more specifically, to a plasma arc torch and method using a contact starting system employing an electrode and a resiliently biased, translatable nozzle or swirl ring.
  • a plasma arc torch generally includes a torch body, an electrode mounted within the body, a nozzle with a central exit orifice, electrical connections, passages for cooling and arc control fluids, a swirl ring to control the fluid flow patterns, and a power supply.
  • the torch produces a plasma arc, which is a constricted ionized jet of a plasma gas with high temperature and high momentum.
  • Gases used in the torch can be non-reactive (e.g. argon or nitrogen), or reactive (e.g. oxygen or air) .
  • a pilot arc is first generated between the electrode (cathode) and the nozzle (anode) .
  • the pilot arc ionizes gas passing through the nozzle exit orifice. After the ionized gas reduces the electrical resistance between the electrode and the workpiece, the arc transfers from the nozzle to the workpiece.
  • the torch may be operated in this transferred plasma arc mode, which is characterized by the conductive flow of ionized gas from the electrode to the workpiece, for the cutting of the workpiece.
  • HFHV high frequency, high voltage
  • the HFHV signal is typically provided by a generator associated with the power supply.
  • the HFHV signal induces a spark discharge in the plasma gas flowing between the electrode and the nozzle, and this discharge provides a current path.
  • the pilot arc is formed between the electrode and the nozzle with the voltage existing across them.
  • contact starting is advantageous because it does not require high frequency equipment and, therefore, is less expensive and does not generate electromagnetic interference.
  • the electrode is manually placed into electrical connection with the workpiece. A current is then passed from the electrode to the workpiece and the arc is struck by manually backing the electrode away from the workpiece.
  • the electrode is supported in part by a spring which maintains intimate electrical and physical contacts between the electrode and nozzle to seal the exit orifice until such time as the pressure in the plasma chamber overcomes the biasing load of the spring.
  • Degradation of the spring due to cyclic mechanical and/or thermal fatigue lead to change of the spring rate or spring failure and, consequently, difficulty in initiating the pilot arc with a concomitant reduction in torch starting reliability.
  • the spring should be replaced periodically; however, due to the location of the spring in the torch body, additional disassembly effort is required over that necessary to replace routine consumables such as the electrode and nozzle.
  • a special test fixture will typically also be needed to assure proper reassembly of the torch. Further, during repair or maintenance of the torch, the spring may become dislodged or lost since the spring is a separate component. Reassembly of the torch body without the spring or with the spring misinstalled may result in difficulty in starting or extended operation of the torch prior to pilot arc initiation.
  • sliding contact portions of the electrode and proximate structure which may be characterized as a piston/cylinder assembly, may be subject to scoring and binding due to contamination.
  • These surfaces are vulnerable to dust, grease, oil, and other foreign matter common in pressurized gases supplied by air compressors through hoses and associated piping. These contaminants diminish the length of trouble free service of the torch and require periodic disassembly of the torch for cleaning or repair. It would therefore be desirable for moving components and mating surfaces to be routinely and easily replaced before impacting torch starting reliability. Accordingly, there exists a need to provide a plasma arc torch contact start configuration which improves upon the present state of the art.
  • the apparatus includes a torch body in which an electrode is mounted fixedly.
  • a translatable nozzle is mounted coaxially with the electrode forming a plasma chamber therebetween.
  • the nozzle is resiliently biased into contact with the electrode by a spring element .
  • a retaining cap is attached to the torch body to capture and position the nozzle.
  • the spring element is a separate component, being assembled in the torch after insertion of the nozzle and prior to attachment of the retaining cap.
  • the spring element is attached to the nozzle, forming an integral assembly which is meant to be replaced as an assembly and not further disassembled by the user.
  • the spring element is attached to the retaining cap, forming an integral assembly therewith.
  • both the electrode and nozzle are mounted fixedly in combination with a translatable segmented swirl ring.
  • An electrically conductive portion of the swirl ring is biased into contact with the electrode by a spring element, which may be a separate component or form an integral assembly with any of the nozzle, retaining cap or swirl ring.
  • the spring element may be any of a variety of configurations including, but not limited to, a wave spring washer, finger spring washer, curved spring washer, helical compression spring, flat wire compression spring, or slotted conical disc.
  • the translatable component is biased into contact with the fixed electrode by the spring element in the assembled state.
  • gas is provided to the plasma chamber having sufficient flow rate and pressure to overcome the biasing force of the spring element, resulting in a pilot arc condition upon translation of the component away from the electrode.
  • the arc may then be transferred to a metallic workpiece in the conventional manner for subsequent processing of the workpiece as desired.
  • the invention provides more reliable plasma torch contact starting.
  • prior art designs employing a movable electrode and fixed nozzle, there are often additional moving parts and mating surfaces such as a plunger and an electrically insulating plunger housing.
  • These parts are permanently installed in the plasma torch in the factory and are not designed to be maintained in the field during the service life of the torch, which may be several years.
  • These parts are subject to harsh operating conditions including rapid cycling at temperature extremes and repeated mechanical impact .
  • the torch working fluid is compressed air, the quality of which is often poor.
  • One significant advantage of this invention is the use of moving parts and mating surfaces which are routinely replaced as consumable components of the torch.
  • the invention also provides enhanced conductive heat transfer from the hot electrode to cool it more efficiently.
  • the electrode which is the most highly thermally stressed component of the plasma torch, is securely fastened to adjacent structure which acts as an effective heat sink.
  • the intimate contact greatly reduces interface thermal resistivity and improves electrode conductive cooling efficiency.
  • the better cooled electrode will generally have a longer service life than a prior art electrode subject to similar operating conditions.
  • FIG. 1A is a schematic partially cut away sectional view of a plasma arc torch working end portion in a de-energized mode in accordance with a first embodiment of the present invention
  • FIG IB is a schematic sectional view of the plasma arc torch working end portion depicted in FIG. 1A in a pilot arc mode in accordance with a first embodiment of the present invention
  • FIG. 2A is a schematic side view of a nozzle with integral spring element in accordance with a first embodiment of the present invention
  • FIG. 2B is a schematic side view of the nozzle depicted in FIG. 1A in a preload assembled state in accordance with this embodiment of the present invention
  • FIG. 2C is a schematic side view of the nozzle depicted in FIG. IB in a pressurized assembled state in accordance with this embodiment of the present invention
  • FIG. 3A is a schematic side view of a partially assembled nozzle with integral spring element in accordance with another embodiment of the present invention
  • FIG. 3B is a schematic side view of the nozzle depicted in FIG. 3A after completion of assembly in accordance with this embodiment of the present invention
  • FIG. 4A is a schematic partially cut away sectional view of a plasma arc torch working end portion in a de-energized mode in accordance with yet another embodiment of the present invention
  • FIG. 4B is a schematic partially cut away sectional view of the plasma arc torch working end portion depicted in FIG. 4A in a pilot arc mode in accordance with this embodiment of the present invention
  • FIG. 4C is a schematic sectional view of the retaining cap depicted in FIG. 4A prior to assembly in the plasma arc torch in accordance with this embodiment of the present invention
  • FIGS. 5A-5F are schematic plan and side views of six exemplary spring elements in accordance with various embodiments of the present invention.
  • FIG. 6A is a schematic partially cut away sectional view of a plasma arc torch working end portion in a de-energized mode in accordance with a further embodiment of the present invention
  • FIG 6B is a schematic sectional view of the plasma arc torch working end portion depicted in FIG. 6A in a pilot arc mode in accordance with this embodiment of the present invention
  • FIG. 7 is a schematic side view of a nozzle with integral spring element in accordance with a still another embodiment of the present invention.
  • FIG. 8A is a schematic sectional view of a plasma arc torch working end portion in a de-energized mode in accordance with an additional embodiment of the present invention.
  • FIG 8B is a schematic sectional view of the plasma arc torch working end portion depicted in FIG. 8A in a pilot arc mode in accordance with this embodiment of the present invention
  • FIG. 9A is a schematic partially cut away sectional view of a plasma arc torch working end portion in a de-energized mode in accordance with still another embodiment of the present invention
  • FIG 9B is a schematic sectional view of the plasma arc torch working end portion depicted in FIG. 9A in a pilot arc mode in accordance with this embodiment of the present invention.
  • FIG. 1A Depicted in FIG. 1A is a schematic partially cut away sectional view of the working end portion of a dual flow plasma arc torch 10 in a de-energized mode in accordance with a first embodiment of the present invention.
  • the term "de-energized” describes the configuration of the torch components prior to pressurization of the plasma chamber. This configuration is also consistent with the unpowered, assembled condition.
  • the torch 10 includes a generally cylindrical body 16 and an electrode 12 which is fixedly mounted along a centrally disposed longitudinal axis 14 extending through the body 16 and the torch 10. Unless otherwise specified, the components of the torch 10 each have a respective longitudinal axis of symmetry and are assembled generally colinearly along the longitudinal axis 14 of the torch 10.
  • the electrode 12 is isolated electrically from the torch body 16 which may serve as a handgrip for manually directed workpiece processing or as a mounting structure for use in an automated, computer controlled cutting or marking system.
  • the nozzle 18 is manufactured as an integral assembly of three components : a generally cylindrical hollow member 20; a spring element 26; and a retainer collar 28.
  • the generally cylindrical hollow member 20 has an open end portion for receiving the electrode 12 and a closed end portion with a centrally disposed orifice 22 for discharge of high energy plasma during torch operation.
  • the exterior of the nozzle member 20 includes a radially extending flange 24 forming a reaction surface for the spring element 26.
  • the nozzle 18 includes a retainer collar 28 having an outwardly disposed flange 30.
  • the collar 28 serves several functions including limiting translational travel of the nozzle member 20 in the torch 10 and capturing the spring element 26 with the flange 30 as part of the integral assembly of the nozzle 18.
  • the collar 28 may be attached to the exterior portion of the member 20 by diametral interference fit or any other conventional method such as mechanical threading, thermal brazing, etc.
  • the nozzle 18 is secured in the torch 10 by means of a retaining cap 32.
  • the cap 32 may be attached to the body 16 by a threaded or other conventional connection to facilitate disassembly of the torch 10 to replace consumables.
  • the cap 32 includes a hollow frustoconical outer shell 34 and a preload ring 36 coaxially disposed therein.
  • the annular preload ring 36 circumscribes the nozzle 18 and includes an interior longitudinally disposed step 38 which abuts spring element 26 and provides additional spring element compression or preload in the assembled state.
  • the interior configuration of the nozzle 18 is sized to provide radial clearance when disposed proximate the electrode 12, forming plasma chamber 40 therebetween.
  • a controlled source of pressurized gas (not depicted) in fluid communication with the chamber 40 provides the requisite gas to be converted into a high energy plasma for workpiece processing.
  • the pressurized gas in the chamber 40 also reacts against the biasing effect of the spring element 26 and is employed to translate the nozzle 18 relative to the electrode 12 during initiation of the pilot arc as depicted in FIG. IB.
  • a low level electrical current is provided serially through the electrode 12 and abutting nozzle 18 as depicted in FIG. 1A.
  • gas is provided to the plasma chamber 40 having sufficient flow rate and pressure to overcome the bias of spring element 26, resulting in a pilot arc condition upon separation of the electrode 12 and nozzle 18.
  • gas would also be provided to the annulus 41 disposed between the interior of shell 34 and proximate exterior surfaces of nozzle member 20 and preload ring 36.
  • the nozzle 18 has moved in a downward direction, providing axial and radial clearance relative to the electrode 12.
  • the nozzle 18 is limited by abutment of the nozzle collar flange 30 with a second longitudinal step 42 of the preload ring 36.
  • the nozzle 18 remains displaced for the duration of operation of the torch 10 in both pilot arc and transferred arc modes .
  • the flow of gas to plasma chamber 40 and annulus 41 is terminated.
  • the spring element force becomes dominant and the nozzle 18 translates upward into abutting relation with the electrode 12.
  • the spring element 26 be electrically conductive, non-oxidizing, and maintained in intimate contact with the nozzle flange 24 and preload ring 36 during nozzle translation.
  • the spring element 26 substantially eliminates micro-arcing between sliding surfaces of the flange 24 and preload ring 36 caused by stray electrical discharges which tend to increase sliding friction therebetween.
  • FIGS. 2A-2C depict the nozzle 18 in three respective states: as an integral assembly prior to insertion in the torch 10; in a preloaded state after insertion in the torch 10 but prior to pressurization of the plasma chamber 40; and after insertion in the torch 10 subsequent to pressurization of the plasma chamber 40.
  • a slight compression of the spring element 26 may be desirable to ensure proper seating of spring element ends against member flange 24 and collar flange 30.
  • Spring element 26 is thereby axially captured at both flanges 24, 30.
  • the depiction of spring element 26 is schematic in nature and may include solely a single biasing element or a plurality of similar or dissimilar stacked elements.
  • the spring element 26 is compressed further by step 38 of preload ring 36.
  • step 38 of preload ring 36 By changing the relative dimension of the step 38, the amount of preload and concomitantly the amount of pressure required in the plasma chamber 40 to separate the nozzle 18 from the electrode 12 can be varied. Note the longitudinal clearance between the collar flange 30 and the preload ring 36 which limits translational travel of the nozzle 18. This clearance determines the gap between the electrode 12 and nozzle 18 upon pressurization of the plasma chamber 40.
  • the clearance dimension should be large enough to provide a sufficient gap between the electrode 12 and nozzle 18 so that a stable pilot arc may form; however, the dimension must not be so large that the gap between the electrode 12 and nozzle 18 becomes too great and available open circuit voltage provided by the power supply becomes inadequate to sustain the pilot arc.
  • a typical range of nozzle travel is between about 0.010 inches (0.254 mm) and about 0.100 inches (2.54 mm), depending on the amperage rating of the torch. For example, for a 20 ampere torch, nominal nozzle travel may be about 0.015 inches (0.381 mm) and for a 100 ampere torch, nominal nozzle travel may be about 0.065 inches (1.651 mm) . For higher current torches, nominal nozzle travel will typically be greater.
  • FIG. 2C depicts the relative position of the nozzle 18 and preload ring 36 during torch operation with the nozzle 18 at the limit of travel, the collar flange 30 abutting the ring 36.
  • typical preload length in the assembled torch 10 would be 0.130 inches (3.30 mm), corresponding to a preload force of about 2.40 pounds (1.09 kg).
  • length of the spring element 26 at full nozzle travel would be about 0.115 inches (2.92 mm), corresponding to a spring force of about 3.12 pounds (1.42 kg) .
  • the pneumatic force is about 6.08 pounds (2.76 kg), almost twice the 3.12 pounds (1.42 kg) of force required to overcome the spring force .
  • the nozzle 18 will be translated reliably during contact starting and maintained at full travel during torch operation.
  • nozzle 18 By making the nozzle 18 an integral assembly of member 20 and spring element 26, replacement and renewal of spring element 26 is assured whenever the nozzle 18 is replaced. Accordingly, starting system reliability is not impaired by thermal or mechanical degradation of the spring element 26, and misassembly of the torch 10 without the spring element 26 is avoided.
  • FIGS. 3A-3B Other methods of retaining the spring element 26 as part of the integral assembly nozzle 18 are provided hereinafter.
  • the exterior of the nozzle 118 includes a radially extending flange 124 forming both a retention and a reaction surface for spring element 126.
  • flange 124 Prior to assembly, includes a longitudinally extending lip 44 which may be circumferentially continuous or formed as a series of discrete, contiguous tabs.
  • the spring element 126 is axially retained by plastically deforming the lip 44 around a proximate portion of the element 126 as depicted in FIG. 3B.
  • Translational travel of the nozzle 118 when assembled in the torch 10 is limited by nozzle body step 46 or other similar feature integrally formed therein.
  • the step 46 abuts similarly against preload ring 36 at plasma chamber pressurization as described hereinabove with respect to travel of nozzle 18.
  • FIGS. 4A-4C desired functionality is achieved by combining the spring element as a component of the retaining cap or preload ring, instead of the nozzle, as shown in FIGS. 4A-4C.
  • the torch 110 includes a centrally disposed electrode 112 and nozzle 218.
  • the nozzle 218 may be of unitary construction and includes a radially extending flange 224 which acts a reaction surface for spring element 226.
  • the nozzle 218 is captured in the torch 110 by a retaining cap 132.
  • the cap 132 includes a hollow frustoconical outer shell 134 which captures preload ring 136 coaxially disposed therein.
  • the preload ring 136 includes an annular groove 48 along an interior portion thereof, sized and configured to receive therein spring element 226. Due to the compliant nature of the spring element 226, the preload ring 136 may be manufactured of unitary construction and the spring element 226 thereafter inserted in the groove 48. Absent direct attempt to pry the spring element 226 from the groove 48, the spring element 226 will be retained in the preload ring 136 and may be considered an integral assembly for the purposes disclosed herein.
  • the nozzle 218 is first disposed over the electrode 112, followed by the preload ring 136 with integral spring element 226.
  • the shell 134 is thereafter attached to the torch body 116.
  • the nozzle 218 is biased into abutting relation with the electrode 112 by the reaction of spring element 226 against nozzle flange 224.
  • Nozzle 218 is longitudinally translatable away from the electrode 112 under pressure in plasma chamber 140, the distance regulated by the clearance between nozzle step 146 and preload ring step 142.
  • this assembly clearance is predetermined to ensure reliable initiation and maintenance of the pilot arc.
  • FIG. 4B depicts the relative position of the nozzle 218 at full travel in the pressurized, pilot arc state. Note, relative to FIG. 4A, compression of the spring element 226, longitudinal clearance between the nozzle 218 and electrode 112, and abutment of nozzle step 146 with preload ring step 142.
  • FIG. 4C is a schematic sectional view of the retaining cap 132 depicted in FIG. 4A prior to assembly in the torch 110.
  • the retaining cap 132 may be manufactured of unitary construction or as an assembly with the integral spring element 226. Alternatively, the cap 132 may be manufactured as a shell 134 and mating preload ring 136. Additional desirable features for the proper functioning of the torch 110 may be readily incorporated, for example, gas circuits for feeding the flow in annulus 141. Providing discrete components to form the cap 132 facilitates use of matched sets of electrodes 112, nozzles 218, and preload rings 136 with a common outer shell 134 to accommodate different power levels and applications.
  • Whether to incorporate a spring element as an integral part of a nozzle assembly or cap (or preload ring) may be influenced by the useful lives of the components. It is desirable to replace the spring element prior to degradation and therefore it may be incorporated advantageously in a component with a comparable or shorter usable life.
  • any of a variety of spring configurations may be employed to achieve the desired biasing function of the spring element .
  • One desirable feature is the capability of the spring element to withstand the high ambient temperatures encountered in the working end portion of a plasma arc torch 10.
  • Another desirable feature is the capability to predict usable life as a function of thermal and/or mechanical cycles. Accordingly, the material and configuration of the spring element may be selected advantageously to provide reliable, repeatable biasing force for the plasma chamber gas pressures employed for the useful lives of the integral nozzle or retaining cap.
  • FIGS. 5A-5F several embodiments of spring configurations which may be employed to achieve the aforementioned functionality are depicted. These embodiments are exemplary in nature and are not meant to be interpreted as limiting, either in source, material, or configuration.
  • FIG. 5A shows schematic plan and side views of a resilient component commonly referred to as a wave spring washer 26a, conventionally used in thrust load applications for small deflections with limited radial height.
  • the washer 26a has a generally radial contour,* however, the surface undulates gently in the longitudinal or axial direction.
  • the washer 26a is available in high-carbon steel and stainless steel from Associated Spring, Inc., Maumee, OH 43537.
  • FIG. 5B schematic plan and side views are provided of a resilient component commonly referred to as a finger spring washer 26b, conventionally used to compensate for excessive longitudinal clearance and to dampen vibration in rotating equipment.
  • the washer 26b has a discontinuous circumference with axially deformed outer fingers .
  • the washer 26b is available in high carbon steel from Associated Spring, Inc.
  • FIG. 5C shows schematic plan and side views of a resilient component commonly referred to as a curved spring washer 26c, typically used to compensate for longitudinal clearance by exertion of low level thrust load.
  • the washer 26c has a radial contour and a bowed or arched surface along an axial direction.
  • the washer 26c is available in high-carbon steel and stainless steel from Associated Springs, Inc. As depicted in FIG.
  • FIG. 5D schematic plan and side views are provided of a resilient component commonly referred to as a flat wire compression spring 26d of the crest-to-crest variety.
  • the spring 26d has a radial contour and a series of undulating flat spring turns which abut one another at respective crests .
  • This particular embodiment includes planar ends and is available in carbon steel and stainless steel from Smalley Steel Ring Company, Wheeling, IL 60090.
  • FIG. 5E shows schematic plan and side views of a common helical compression spring 26e, the side view depicting both free state and compressed contours.
  • the spring 26e has squared, ground ends and is available from Associated Spring, Inc. in music wire for ambient temperature applications up to about 250° F (121° C) and stainless steel for ambient temperature applications up to about 500° F (260° C) .
  • FIG 5F schematic plan and side views are provided of a resilient component known as a slotted conical disc or RINGSPA NTM Star Disc 26f, commonly employed to clamp an internally disposed cylindrical member relative to a circumscribed bore or to retain a member on a shaft.
  • the disc 26f has a radial contour with alternating inner and outer radial slots and a shallow conical axial contour which provides the desired biasing force for use as a spring element . Stiffness is a function of both disc thickness and slot length.
  • Disc 26f is available in hardened spring steel from Powerhold, Inc., Middlefield, CT 06455.
  • FIG. 6A depicts a schematic partially cut away sectional view of the working end portion of an air cooled plasma arc torch 210 in a de-energized mode in accordance with a further embodiment of the present invention.
  • the torch 210 includes a nozzle 218 biased into abutting relationship with a centrally disposed electrode 212 by spring element 326, depicted here as a helical compression spring.
  • the nozzle 218 is of unitary construction and includes a longitudinal step 246 on flange 324 against which spring element 326 reacts. Spring element 326 also reacts against step 138 of retaining cap 232.
  • Nozzle 218 further includes a radially extending flange 50 radially aligned with cap step 238, the longitudinal clearance therebetween defining the limit of travel of the nozzle 218 when plasma chamber 240 is fully pressurized.
  • the nozzle 218 is disposed over the mounted electrode 212, the spring element 326 is inserted and the retaining cap 232 attached to the body 216 by a threaded connection or other means.
  • the free state length of spring element 326 and assembled location of cap step 138 and nozzle step 246 are predetermined to ensure the desired spring element preload at assembly.
  • the torch 210 also includes a gas shield 52 which is installed thereafter for channeling airflow around the nozzle 218.
  • the torch 210 includes an optional insulator 54 disposed radially between retaining cap 232 and nozzle flange 324.
  • the insulator 54 may be affixed to the retaining cap 232 by radial interference fit, bonding, or other method and should be of a dimensionally stable material so as not to swell or deform measurably at elevated temperatures .
  • An exemplary material is VESPELTM, available from E.I. du Pont de Nemours & Co., Wilmington, DE 19898.
  • a helical metal compression spring with flat ground ends may be employed as depicted.
  • the spring should be made of a non- oxidizing material such as stainless steel and need only support initial current flow between the nozzle 218 and retainer 232 during nozzle translation because at full nozzle travel, nozzle step 246 abuts retaining cap step 238 as depicted in FIG. 6B.
  • the torch configuration in the pilot arc state with the plasma chamber 240 pressurized and the nozzle 218 at full travel is depicted in FIG. 6B .
  • a substantially integral assembly of the spring 26e and nozzle cylindrical member 120 can be achieved as depicted in nozzle 318 in FIG. 7.
  • the nominal diameter of the member 120 is increased proximate the nozzle flange 424 against which the spring 26e abuts to create a radial interference fit therewith.
  • the remainder of the member 120 has a nominal diameter less than the nominal bore of the spring 26e. Accordingly, once the spring 26e has been seated on the member 120, the spring 26e is firmly retained, cannot be misplaced or left out of the assembly, and can be replaced as a matter of course when the nozzle 318 is replaced. Referring now to FIG.
  • plasma arc torch 310 is depicted in a de-energized mode in accordance with an additional embodiment of the present invention.
  • the torch 310 includes a centrally disposed electrode 312 having a spiral gas flow passage 56, of the type disclosed in the 871 patent, machined into a radially enlarged shoulder portion thereof .
  • the electrode 312 is mounted fixedly in the torch 310, which also includes a translatable nozzle 418.
  • the nozzle 418 may be of unitary construction and includes a radially extending flange 524 which acts a reaction surface for spring element 426, depicted here schematically as a "Z" in cross-section. Spring element 426 also reacts against step 338 of retaining cap 332.
  • Nozzle 418 further includes a radially extending step 346 radially aligned with cap step 338, the longitudinal clearance therebetween defining the limit of travel of the nozzle 418 when plasma chamber 340 is fully pressurized.
  • the nozzle 418 is disposed over the helically grooved mounted electrode 312 and swirl ring 58, the spring element 426 is inserted and the retaining cap 332 attached to the body 316 by a threaded connection.
  • the free state length of spring element 426 and assembled location of cap step 338 and nozzle flange 524 are predetermined to ensure the desired spring element preload at assembly.
  • Torch 310 also includes a gas shield 152 which is installed thereafter for channeling airflow around the nozzle 418.
  • the spring element 426 may be a separate component, as depicted, or may be attached to either the nozzle 418 at flange 524 or retaining cap 332 proximate step 338 by any method discussed hereinabove, depending on the type of spring employed.
  • the torch 310 is depicted in the pilot arc state.
  • Pressurization of plasma chamber 340 causes longitudinal translation of the nozzle 418 away from electrode 312, compressing spring element 426.
  • Plasma gas pressure and volumetric flow rate are sufficiently high to compress spring element 426 while venting gas to ambient through orifice 122 and aft vent 60 after passing through spiral passage 56.
  • Reference is made to the ⁇ 871 patent for further detail related to the sizing of the spiral passage to develop the desired pressure drop across the electrode 312.
  • the passage 56 both enhances cooling of the electrode and develops back pressure to facilitate pressurization of plasma chamber 340 and translation of the nozzle 418.
  • nozzle step 346 abuts retaining cap step 338.
  • FIG. 9A is a schematic partially cut away sectional view of a working end portion of plasma arc torch 410 in a de-energized mode in accordance with another embodiment of the present invention.
  • Both electrode 412 and nozzle 518 are mounted fixedly in torch 410 with swirl ring 158 disposed therebetween to channel gas flow into plasma chamber 440 at the desired flow rate and orientation.
  • Swirl ring 158 includes three components: aft ring 62, center ring 64 and forward ring 66.
  • Aft and forward rings 62, 66 are manufactured from an electrically insulating material while center ring 64 is manufactured from an electrically conductive material such as copper.
  • Spring element 526 reacts against radially outwardly extending nozzle flange 624 and swirl center ring flange 130.
  • Retaining cap 432 preloads the spring element 526 at assembly and ensures intimate contact between aft facing step 438 of center ring 64 and forward facing step 446 of electrode 412.
  • current is passed through the electrode 412, center ring 64, spring element 526, and nozzle 518.
  • center ring 64 translates toward the nozzle 518, compressing spring element 526 and drawing a pilot arc proximate the contact area of steps 438, 446.
  • leg 68 of center ring 64 abuts step 242 of nozzle 518 making electrical contact therewith.
  • the pilot arc transfers from the center ring 64 to the nozzle 518 and may thereafter be transferred to a workpiece in the conventional manner.
  • the center ring 64 may be translated quickly to ensure that the center ring 64 reaches the nozzle 518 before the pilot arc.
  • the acceleration of the swirl ring 64 (ignoring friction of bearing surfaces) is about 21,950 ft/sec 2 (6690 m/sec 2 ) .
  • travel time will be about 3.9 x 10 "4 sec.
  • the pilot arc travels longitudinally at the same velocity as the plasma gas. Accordingly, for a plasma gas volumetric flow rate of 0.5 ft 3 /min (2.36 x 10 "4 m 3 /sec) , passing through the annular plasma chamber 440 having a cross- sectional area of about 0.038 square inches (2.43 x 10 "5 m 2 ) , the velocity of the gas and pilot arc will be about 31.8 ft/sec (9.7 m/sec) .
  • the distance the arc will travel on the center swirl ring 64 in the 3.9 x 10 " sec of swirl ring travel will be about 0.149 inches (3.8 mm). As long the metallic center swirl ring 64 is at least 0.149 inches (3.8 mm) in longitudinal length, the center swirl ring 64 will land on the nozzle 518 before the pilot arc reaches the end of the swirl ring 64.
  • the spring element 526 is a separate component; however, the center ring 64 or nozzle 518 could be modified readily to make the spring element an integral component therewith.
  • the external diameter of the nozzle 518 proximate flange 624 could be enlarged to create a diametral interference fit with spring element 526.
  • the swirl ring diameter proximate flange 130 could be enlarged.
  • the spring element 526 could be retained by the retaining cap 432 by modifying the interior thereof with a groove, reduced diameter, or other similar retention feature.
  • water cooling of the nozzle 518 could be added for high nozzle temperature applications such as powder coating.
  • torch 410 includes a gas shield 252, the torch 410 could be operated without the shield 252 to reach into workpiece corners or other low clearance areas. Since the translating components are disposed within the retaining cap 432, they would not be subject to dust, debris, and cutting swarf which might tend to contaminate sliding surfaces and bind the action of the contact starting system.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Plasma Technology (AREA)
  • Arc Welding In General (AREA)

Abstract

L'invention a trait à un procédé ainsi qu'à la structure correspondante permettant de démarrer par contact un chalumeau à arc de plasma. Un composant conducteur transportable, une buse ou un anneau à turbulence, est mis en contact avec une électrode par un élément compliant constituant un ressort. Un arc pilote se forme tout d'abord par le passage d'un courant à travers l'interface électrode/composant. Le composant est ensuite transféré par le gaz sous pression dans une chambre à plasma constituée entre l'électrode et ledit composant, chambre dans laquelle le débit est assez fort pour comprimer l'élément compliant constituant un ressort et donner naissance à l'arc pilote. Cet élément peut être un élément séparé, être partie intégrante de la buse ou de l'anneau à turbulence ou encore faire partie d'un capuchon de maintien, ce qui facilite l'enlèvement et le remplacement dudit élément constituant un ressort par des pièces consommables du chalumeau.
PCT/US1997/016318 1996-10-08 1997-09-17 Chalumeau a arc de plasma et procede utilisant un systeme de demarrage a contact WO1998016090A1 (fr)

Priority Applications (5)

Application Number Priority Date Filing Date Title
JP51753598A JP4267704B2 (ja) 1996-10-08 1997-09-17 プラズマアークトーチ、並びに接触始動システムを用いた方法
CA002268102A CA2268102C (fr) 1996-10-08 1997-09-17 Chalumeau a arc de plasma et procede utilisant un systeme de demarrage a contact
EP97943315A EP0941640B1 (fr) 1996-10-08 1997-09-17 Chalumeau a arc de plasma et procede utilisant un systeme de demarrage a contact
DE69737201T DE69737201T2 (de) 1996-10-08 1997-09-17 Lichtbogen-plasmabrenner und verfahren, der ein kontaktstartsystem verwendet
AU44814/97A AU727927B2 (en) 1996-10-08 1997-09-17 Plasma arc torch and method using contact starting system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/727,028 US5994663A (en) 1996-10-08 1996-10-08 Plasma arc torch and method using blow forward contact starting system
US08/727,028 1996-10-08

Publications (1)

Publication Number Publication Date
WO1998016090A1 true WO1998016090A1 (fr) 1998-04-16

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PCT/US1997/016318 WO1998016090A1 (fr) 1996-10-08 1997-09-17 Chalumeau a arc de plasma et procede utilisant un systeme de demarrage a contact

Country Status (7)

Country Link
US (1) US5994663A (fr)
EP (2) EP1765045B1 (fr)
JP (1) JP4267704B2 (fr)
AU (1) AU727927B2 (fr)
CA (1) CA2268102C (fr)
DE (1) DE69737201T2 (fr)
WO (1) WO1998016090A1 (fr)

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CN1311947C (zh) * 2001-02-27 2007-04-25 热动力股份有限公司 接触起动的等离子体焊炬及起动该焊炬的方法

Also Published As

Publication number Publication date
EP0941640B1 (fr) 2007-01-03
AU4481497A (en) 1998-05-05
JP4267704B2 (ja) 2009-05-27
DE69737201D1 (de) 2007-02-15
AU727927B2 (en) 2001-01-04
DE69737201T2 (de) 2007-11-08
EP1765045B1 (fr) 2011-07-27
EP1765045A2 (fr) 2007-03-21
EP0941640A1 (fr) 1999-09-15
CA2268102A1 (fr) 1998-04-16
EP1765045A3 (fr) 2007-09-26
CA2268102C (fr) 2002-07-02
JP2001502110A (ja) 2001-02-13
US5994663A (en) 1999-11-30

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